Vegetation documented more than 70 natural and semi-natural plant associations recorded in the Biebrza valley. Some of the most dominating and ecologically valuable of these associations include sedge, sedge-moss, reed communities, and mineral islands. The most dominant forest associations include black alder, swampy birch, and peat coniferous forests. Hydrogenic dependent habitats cover 40% of the valley`s total area, and these representative water ecosystems are riverbeds and numerous oxbows or old riverbeds. Changes of the environmental condition cause by the Augustowski Channel construction, together with land amelioration done in the 60`s induce permanent decreasing of the ground water table. This decrease of the ground level gave way to many semi-natural communities the most common being meadow type associations. Frequent anthropogenic ecosystems found in the valley are pastures, cultivated grounds and urbanized areas with plant communities surrounding the Osowiec Fortress being by far the most important.